As operation of an oil well proceeds, a technique used for extraction of petroleum changes in the course of time. In most cases, extraction in its beginning is carried out owing to the natural pressure existing in a producing formation (flowing well operation mode). With the passage of time, the formation pressure falls, and for this reason the equipment for mechanised extraction of petroleum must be applied.
Presently, production of petroleum can be carried out by successive development of separate producing formations, if a given well intersects a number of beds eventually suitable for petroleum production. A disadvantage of this technique consists in that when the change-over from one formation to another takes place, a considerable amount of time has to be spent, and additional expenses are needed to re-adjust the equipment. Furthermore, as a given producing formation is developed, the extracted petroleum volume may diminish, which results in a significant decrease in productive capacity of a well. Under these circumstances, continuation of extraction of petroleum out of this formation may cause lowering of cost-effectiveness of a well, and the change-over to development of a subsequent formation results in incomplete exhaustion of this previous formation. Another disadvantage of such successive development consists in that, due to absence of data on extraction from other formations, productive capacity of a given well and, consequently, economic advisability of development of a given well is hard to be forecast.
It should be further noted that the equipment used at the stage of flowing well operation, and the equipment used for the mechanised production must be different. For this reason, when a petroleum extraction technique is changed, the flowing-well equipment if lifted and replaced with that for the mechanised petroleum extraction. Such replacement of equipment requires a considerable time and represents a rather expensive operation, especially for offshore wells.
Another extraction technique is a mixed extraction out of different formations in the form of single flow, and pumping-out of the same using one downhole pump. When this technique is used, monitoring of origin of the extracted fluids is not possible. Productive capacity of each one of formations depends on such different parameters as pressure, viscosity of fluids, throughput capacity of each one of the formations. In other cases, a formation may start producing too much water or gas. But it is not possible to determine which one of the formations produces these undesirable fluids. Proper monitoring of the formation-by-formation productive capacity is also impossible.
In the mechanised petroleum extraction, the electric immersion pumps have been used most extensively. However, these pumps have some drawbacks:                fast wear of parts due to high rotational speeds and the effects exerted by hard particles contained in the extracted fluid;        poor operation with a gas that restricts capacity of a pump and can even cause failure thereof;        a great length of these pumps makes mounting thereof more difficult and increases the accompanying expenses;        a greater mass of these pumps causes them to be more sluggish;        supply of a fluid through a pump cannot be determined, for such possibility depends on a number of parameters of a given fluid;        a low reliability due to high rotational speed and a considerable mass, and also for the reason that the pump motor has high voltage and there is a strong current in oil, which circumstances may cause a motor to fail.        
In view of the matters discussed above, one of the goals this invention is directed at, is development of a downhole system for extracting the fluids, which system will allow simultaneous extraction of petroleum out of a number of producing formations, the feature of controlling extraction out of each one of formations being provided. The other goal consists in provision of an immersion hydraulic machine for extraction of fluids, which machine will avoid disadvantages of the electric immersion pumps, allow controlling of extraction, and will be suitable for operation both in the flowing well operation mode and the mechanised extraction mode.
This goal is to be attained using a downhole system for extracting the fluids, comprising: a casing pipe and a tubing extending therethrough, between which pipe and tubing formed are separate isolated cavities, each one of them communicating, via perforations, with a corresponding formation; in each one of the isolated cavities, to the tubing coupled is a hydraulic machine comprised by a motor and pump; the hydraulic machines in different isolated cavities being adapted to be controlled independently.
This feature of coordinating a respective hydraulic machine with each one of the producing formations allows develop several producing formations concurrently, and owing to independent controlling of each one of the hydraulic machines—said formations can be developed independently of one another, and with an extraction volume desirable for each one of the formations.
Independent controlling of a respective hydraulic machine can be preferably effected by a separate control unit. A control unit is able to control both supply for motor of a respective hydraulic machine and output of this motor.
Adjustment of the motor supply can be done by changing of the shaft rotational speed. In case a motor is the electric motor, then rotational speed of its shaft can be adjusted using the control unit by changing the supply current frequency, strength of current, voltage, etc. A method for adjusting the speed depends on a motor type, for example: changing of frequency is most frequently used to adjust the three-phase alternating current electric motors, while adjustment of the input voltage is more used to control speed of the direct current electric motors. Means and methods for such adjustment of electric motors are generally known in prior art, and are not described here in more detail. If a number of motors is positioned in one well, then required is the independent controlling, which can be done by provision of independent cables for each motor from the surface. If a motor is the hydraulic motor, then the shaft rotational speed can be adjusted using the control unit by changing a quantity, rate, etc. of the working fluid supplied to the motor.
To carry out said adjustment of the hydraulic motor, the control unit can comprise a controlled throttle and/or permanent throttle, etc. positioned on the hydraulic motor hydraulic line. In the simplest case, the control unit is either a permanent throttle or controlled throttle. The controlled throttles and methods for adjusting the same are generally known in prior art, and are not described here in more detail. These throttles increase the pressure drop in the flow going towards that motor. This pressure increase provides advantage for the flow towards another motor.
A hydraulic machine motor can be implemented in the form of a hydraulic motor wherein the drive shaft is disposed eccentrically with respect to the housing of that hydraulic motor. In this case it may be preferable to adjust volume of a hydraulic motor by adjusting a value of eccentricity. In this case the control unit includes the assembly of rod-hydraulic cylinder, gearing assembly {e.g. rack-gears, etc.), or a similar means adapted to exert action on the motor shaft for changing its eccentricity with respect to the motor housing.